Angular 2 - Checkbox未保持同步

Question

我正在研究Angular 2.0(是的,有点落后于当前的2.4).

我有一个复选框列表.我试图在未检查到最后的复选框时检查所有的复选框.

HTML

<div *ngFor="let filter of filters">
    <label htmlFor="check-box-{{filter.text}}"
           [ngClass]="(filter.selected)? 'active' : '' ">

           <input type="checkbox" 
                 name="check-box-{{filter.text}}"
                 [checked]="filter.selected"
                 (change)="onSelectFilter(filter)"
                 attr.id="check-box-{{filter.text}}">

           {{filter.selected}} -  ({{filter.counter}})

    </label>
</div>

TS

onSelectFilter(filter: Filter){
    filter.toggleSelection();


    let isAnyFilterSelected = this.filters.find(filter => filter.selected);

    // If no filter is selected then ALL filters are selected
    if(!isAnyFilterSelected){
        this.filters.forEach(filter => filter.selected = true );
    }

}

我为它创造了一个plunker.

https://plnkr.co/edit/uzF6Lk5fxRZjXBOaS9ob?p=preview

如果取消选中CHECKED属性为TRUE的唯一复选框,我希望所有复选框都具有CHECKED属性.这不会发生.

有任何想法吗？

Answer 1

你应该使用ngModel而不是绑定checked,并使用setTimeout.

<div *ngFor="let filter of filters">
    <label htmlFor="check-box-{{filter.text}}"
           [ngClass]="(filter.selected)? 'active' : '' ">

           <input type="checkbox" 
                 name="check-box-{{filter.text}}"
                 [ngModel]="filter.selected"
                 (ngModelChange)="onSelectFilter($event,filter)"
                 attr.id="check-box-{{filter.text}}">

           {{filter.selected}} -  ({{filter.counter}})

    </label>
</div>

onSelectFilter(selected:boolean,filter: Filter){
    filter.selected=selected;
    if(this.filters.every(filter=>!filter.selected)){
      setTimeout(()=>{
        this.filters.forEach(filter=>filter.selected=true);
      });
    }
}

plunkr

"为什么需要这么多诡计呢？"

实际上,因为从变换检测器的角度来看,先前状态和新状态之间没有变化.

所以不需要更新@Input()子项/调用()的writeValue()方法.ControlValueAccessor<input type="checkbox" [ngModel]="foo">

使用setTimeout,首先将属性更新为false,然后将其更改延迟回初始状态,从而允许新的更改检测周期.

另请注意,类似事件(ngModelChange)与更改检测周期无关.

没有setTimeout():

在这里,我们将得到与您的示例相同的结果,当我们保持foo为真时,复选框将不会更新:

代码(plunkr):

@Component({
  selector: 'my-app',
  template: `
    <input id="foo" type="checkbox" [ngModel]="foo" (ngModelChange)="fooChange($event)"><label for="foo">{{foo}}</label>
  `,
})
export class App {
  filters:[];
  foo=true
  fooChange(newValue:boolean){
    if(newValue===false)
        this.foo=true; // if newValue is false, foo becomes true
      else
        this.foo = newValue; // otherwise, do change
  }
}

引擎盖下发生了什么:

同 setTimeout()

这次我们将使用以下方法延迟将值重置为下一个刻度setTimeout:

代码(plunkr):

@Component({
  selector: 'my-app',
  template: `
    <input id="foo" type="checkbox" [ngModel]="foo" (ngModelChange)="fooChange($event)"><label for="foo">{{foo}}</label>
  `,
})
export class App {
  filters:[];
  foo=true
  fooChange(newValue:boolean){
    this.foo=newValue; // we need to make it change !
    setTimeout(()=>{
      if(newValue===false)
        this.foo=true; // if newValue is false, foo becomes true
      else
        this.foo = newValue; // otherwise, do change  
    })
  }
}

引擎盖下发生了什么: